Electrohydraulic valve control systems for vehicles and like applications often require not only position control of the system output, but also velocity and/or acceleration control as well. For example, an excavator may require position control of the bucket teeth during a digging cycle, velocity control during other modes of operation, and acceleration control during swing drive. It is conventional to provide separate position, velocity and acceleration sensors for closed loop feedback control during the position, velocity and acceleration demand modes, respectively. However, provision of three transducers adds to the overall cost and complexity of the system.
It is a general object of the present invention to provide an electrohydraulic valve control system wherein position, velocity and/or acceleration control may be obtained while employing only one feedback sensor. In this connection, it has been recognized that position feedback is more readily amenable to operator display and to automation. It is therefore a more specific object of the invention to provide an electrohydraulic valve control system which employs a position sensor and feedback loop and is adapted to function in the velocity and/or acceleration demand control modes.
Another object of the invention is to provide an electrohydraulic valve control system of the described character which functions in the velocity or acceleration control modes and which compensates for lag, creep or dead-time in the system output.